Lecture02

Geog 176B Lecture 2: Representing Geography[Text: Ch. 3]: 

Geog 176B Lecture 2: Representing Geography [Text: Ch. 3] http://www.mondodisotto.it/imageiraq/

A map is a representation: 

A map is a representation Geometry is orthographic and scaled Features are symbolized

Why do we use representations?How do we gather information?: 

Why do we use representations? How do we gather information? Limits on human senses Sight Visible spectrum (400-800 nm) LOS, Horizon, Visibility Sound Audible spectrum (50-15K Hz) Range to 100m Taste, touch, smell Rather limited spatial range Limited sensory distinction

Everything else we know about the world we know through communication: 

Everything else we know about the world we know through communication text speech maps photographs radio, TV Internet databases

Knowledge of the surface of the Earth: 

Knowledge of the surface of the Earth 500,000,000 sq km On average 100 sq m is sensed directly at any point in time Odds of being in the right place at the right time p=100/500,000,000,000,000= 0.000 000 000 000 2 Odds are trillions to one Lotto odds are 25.8 million to one Can extend that through migration, travel

Mike Goodchild’s Counties Visited: 

Mike Goodchild’s Counties Visited

5 billion years: 

5 billion years If we live through 70 p=70/5,000,000,000=0.000 000 014 So, we can know almost nothing about the surface of the Earth via our senses alone

We rely on communicated information to:: 

We rely on communicated information to: decide where to go as tourists, shoppers run large corporations manage agriculture, forestry choose where to live Travel from A to B Understand geography!

All such information must use a representation: 

All such information must use a representation What is communicated is a representation of the real thing Locations in time and space are reduced to a few symbols Communication requires simplification The real world is infinitely complex So representations reduce information to a manageable volume

Representations occur:: 

Representations occur: In the human mind, in memory and reasoning (e = m c2) In speech (e.g. acromyns) In written text (abbreviations, etc.) In photographs In digital databases and in GIS

Digital representation: 

Digital representation

Much (most?) human communication is now digital: 

Much (most?) human communication is now digital sent through a "pipe" or transmission channel that can transmit only 0s and 1s stored on devices that can store only 0s and 1s processed as 0s and 1s text in email, word processors uses ASCII (1 & 0) voice in telephone music on CD DVD, digital TV FAX

Digits, distance, and communication: 

Digits, distance, and communication When two humans communicate at a distance, chances are the content is expressed at some point in digital form The further the distance the more likely the communication is digital The longer/denser the communication, the more likely it is digital

Digital: 

Digital From "digit" meaning finger A character in a counting system How many symbols? 0 thru 9, A-Z, a-z, etc. All can reduce to 0 and 1 To all intents and purposes "digital"=“binary”

The digital translation challenge: 

The digital translation challenge How can we express knowledge exclusively in 0s and 1s? How can we describe what we know about the world in 0s and 1s? How do we capture complex earth features as representations?

Digital vs Analog: 

Digital vs Analog analog information expressed by scaling quantities good for quantitative information a paper map is analog world is scaled to a miniature representation representative fraction is key, e.g. 1:24,000 digital information expressed by symbols requires a coding scheme of representation in symbols sender and receiver must agree on the scheme what does digital scale mean?

Digital Coding of Text: 

Digital Coding of Text ASCII code one code per character A = 65, B = 66, etc. 26 letters plus common symbols originally 128, extended to 256 8 binary digits (one byte) per character

Digital equivalents: 

Digital equivalents Images: JPEG, TIFF, GIF, BMP, ... Sound: MIDI, MP3, WAV FAX: CCITT Maps, geographic information: GIS data models and structures

Digital coding schemes important in GIS: 

Digital coding schemes important in GIS ASCII eight bits per character, names, text annotation integer 3 bits per decimal digit, n bits give 2^n options, or 32 bits per whole number (short, long integer) float (single precision) 1 sign bit, 7 exponent bits (-63 to +63), 24 mantissa bits (8 significant digits) double precision 1 sign bit, 7 exponent bits, 56 mantissa bits (18 significant digits) BLOB binary large object

What if you received this message:: 

What if you received this message: 0100 1000 0110 0101 0110 1100 0110 1100 0110 1111 0010 0000 0111 0111 0110 1111 0111 0010 0110 1100 0110 0100

The Message on Voyager <http://voyager.jpl.nasa.gov/spacecraft/goldenrec.html>: 

The Message on Voyager <http://voyager.jpl.nasa.gov/spacecraft/goldenrec.html>

Communication of information via a channel: 

Communication of information via a channel Claude Shannon’s Model C. E. Shannon: A mathematical theory of communication. Bell System Technical Journal, vol. 27, pp. 379–423 and 623–656, July and October, 1948.

How efficient is the channel of communication?: 

How efficient is the channel of communication? Is there information that can't be expressed, e.g. in text What are the limits of a GIS as a communication channel? What information about a place can't be expressed in GIS? Is the message optimally expressed in the coding system? What if the sender and receiver can't understand each other? different language different alphabet different GIS different data model

Geographic Representation: 

Geographic Representation Geographic information information about some place on the surface of the Earth or near the surface at some point in time one of the earliest forms of shared information hunters and gatherers reporting back to the band early stick maps for navigation in the Pacific drawings on cave walls

Ancient geographical representations: 

Ancient geographical representations Source: http://www.khadijateri.com/tribes4.jpg http://bernard.pitzer.edu/~dsegal/1492/FIGURES/ Libyan cave paintings Marshall Islands Stick Chart

And it’s so different today!: 

And it’s so different today!

Enter paper: 

Enter paper the printing press in the 15th Century information accessible to all shared knowledge as a human community asset Book: Prince Henry the Navigator, 1394-1460

Global internet use: 

Global internet use  

An atom of geographic information: 

An atom of geographic information <location, time, attribute> “It's mild today in Santa Barbara” Vs. At 34°25'33" North, 119°42'51" West at noon PST the temperature was 14 Celsius

Standardization: 

Standardization general methods for describing location everyone around the world understands latitude and longitude similarly for time (International Meridian Conference 1884) attributes must also be generally understood “mild" is subjective and relative -14 Celsius is generally understood Did Hugh Grant climb a hill or a mountain?

The Englishman Who Went Up a Hill But Came Down a Mountain (1995): 

The Englishman Who Went Up a Hill But Came Down a Mountain (1995) Two English cartographers visit the small South Wales village of Ffynnon Garw, to measure what is claimed to be the "first mountain inside of Wales". It's 1917, and the war in Europe continues. The villagers are very proud of their "mountain", and are understandably dissapointed and furious to find that it is in fact a "hill". Not to be outwitted by a rule (and the Englishmen who enforce it), the villagers set out to make their hill into a mountain, but to do so they must keep the English from leaving, before the job is done. Source: http://www.imdb.com/title/tt0112966 Hill: A well-defined natural elevation smaller than a mountain.

Suppose we could capture it all: 

Suppose we could capture it all A complete representation of the planet Past, present, and future A "mirror world“ Douglas Adam’s computer for the search for the ultimate question whose answer is 42 AKA Digital Earth

How many atoms are there?: 

How many atoms are there? An infinite number To make a two-word description of every sq km on the planet would require 10 Gigabytes To store one number for every square meter on the planet would require 1 Petabyte (=1000 Terabytes = 1,000,000 gigabytes= 1 billion megabytes That's too many for any current computing system How do we limit file size?

Reduce the level of detail, aggregate, generalize, approximate: 

Reduce the level of detail, aggregate, generalize, approximate Ignore the water that's 2/3 of the planet One temperature for all of California one number for an entire polygon Sample the space only measure at weather stations because temperature varies slowly All geographic data miss detail All are uncertain to some degree

Objects and Fields: 

Objects and Fields Given that (1) we must digitally represent the world to gather (gain) knowledge about it and (2) all representations of the earth are imperfect; then The most important of the options is how we think about (and model) the world Cartographic representation led to the feature model Remote sensing led to the field model Both are useful

The Cartographic Heritage: 

The Cartographic Heritage

Discrete objects: 

Discrete objects Point, lines, areas (or volumes) having known properties Littering an otherwise empty space Objects can be manipulated/edited Objects can be found in the real world Objects may overlap Objects can be counted

Favoring Measurement: Fields: 

Favoring Measurement: Fields Things it's worth measuring at every location on the planet temperature soil pH soil type land cover type elevation rainfall tax rates

Fields: 

Fields Fields contain variables that have one value everywhere The value of the variable is a function of location field = a way of conceiving of geography as a set of variables each having one value at every location on the planet z = f (x , y , z , t)

Can represent one variable as:: 

Can represent one variable as: polygons grids TIN sample points contours

Fields and Objects: 

Fields and Objects Objects are intuitive, part of everyday life Fields are more associated with science and measurement Both objects and fields can be represented either in raster or in vector form Both may need to coexist in a GIS

One geodatabase can have multiple representations of a feature: 

One geodatabase can have multiple representations of a feature